Check Contrast

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, openWorldHint=false, so the safety profile is covered. The description adds an edge-case note about GrayColor's ink-quantity interpretation differing from the API reference, which is valuable domain-specific behavioral context, but does not cover return values or failure modes. With annotations already covering safety, a 3 is appropriate.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Three sentences, front-loaded with the core purpose, then modes, then an important caveat. Zero waste; every sentence earns its place.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given readOnly annotations, 100% schema coverage, and no output schema, the description covers the purpose, modes, and a non-obvious edge case (GrayColor). It's complete enough for an agent to call correctly, though it could mention output format or how WCAG thresholds are reported.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the schema already documents all parameters, including nested color objects with types (cmyk/rgb/gray). The description implies the manual mode requires two color objects, but does not add meaning beyond the schema for individual color properties. Baseline 3 is correct when schema does the heavy lifting.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource: check WCAG color contrast ratios. It distinguishes two operating modes (manual vs auto), which is useful. However, it doesn't differentiate itself from siblings like get_colors or preflight_check, which might relate to color/compliance checks, so sibling differentiation is absent.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicitly describes two usage modes: manual mode requires providing two colors, auto mode detects overlapping pairs. This tells the agent when to use each mode, though it doesn't state when to use this tool versus alternatives like get_colors or preflight_check.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.